In a typical seismic brace for a pipe, a cable is fastened around the pipe and then anchored to the building concrete structure using a bolt and a restraint clip. When the pipe moves from side to side in an earthquake, the cables pull it back into proper position. Pulling down and to the side on the cable assembly applies a combination of loading of the fastener to the building structure with part of the load in shear forces and the other part in tension forces. This combination loading at an angle to the fastener and geometry of the bracket used results in a prying effect on the fastener. The prying effect varies according to the angle to the fastener at which the load is applied.
As can be seen in the prior art drawings, FIGS. 1 and 2. The restraint clip 40, shown in detail in FIG. 1, features a hole in its center 46 wherein a bolt or support rod can be placed as shown in FIG. 2. This particular clip device is manufactured by Loos & Co., Inc. of Naples, Fla. 34104.
In this particular restraint clip 40, the seismic cables 48 are attached to two ears 44 typically placed at 90 degree angles to one another and bent upwards from the horizontal as shown. Cables 48 are attached to the ears by a loop that is formed using oval sleeves 50. Pulling on restraint clip 40 by means of the cable 48, restraint clip 40 can be pried loose.
FIGS. 15 and 16 show a restraint clip 40′ bolted to a concrete structure, but attached to a pipe 41 (or similar rigid article) rather than the cable 48. This particular restraint clip is typical for pipe, angle iron and strut type seismic brace components of other manufacturers. In this particular restraint clip, the seismic brace components are attached to the clip 40′ by a hinge element 43 to allow the rigid pipe 41 to assume various different brace angles from vertical. Whether a flexible cable 48 or rigid pipe 41 is used as a brace component, application of force along the length of the brace component can cause the clip 40, 40′ to pry the bolt out of the concrete. More particularly, the clip 40, 40′ acts as a second class lever. An edge or point F of the clip 40, 40′ on the opposite side of the bolt from the ears 44, 44′ is the fulcrum. The bolt and the location on the ears 44, 44′ where the cable 48 or pipe 41′ are connected are both spaced from the fulcrum F on the same side of the fulcrum. Accordingly, the clip 40, 40′ multiplies the tension force being applied to the bolt to pry it out as shown more specifically in FIG. 16 with respect to the clip 40′.
As noted above, this is due to the fact that the seismic brace components are not pulling directly parallel or perpendicular to the axis of the anchoring bolt or support rod. Instead, a substantial component of the force applied to the brace components end up as both shear force (i.e., a force that is perpendicular to the axis of the bolts) and tension force (i.e., a force that is parallel to the axis of the bolts). The tension portion of this combined shear and tension loading is increased due to the prying effect of the restraint clip. This increased tension force will cause the restraint clip to be pried loose (See FIG. 15). The greater the angle between the seismic brace and the axis of the bolt holding the restraint clip, the greater the tension force (a force that is coincident with the axis of the bolt). In fact, the inventor has found, in a representative example, that at a 30 degree angle, the horizontal allowable earthquake load (Fps) is only 239 pounds when using a “prying” type of clip and with a first embodiment of the applicant's invention (described hereinafter) the horizontal allowable earthquake load is 689 pounds.
There is not found in the prior art that a cable restraint clip or other seismic brace restraint clip that does not increase the tension load on the anchoring bolt due to the prying effect of the restraint clip geometry in order to eliminate premature failure of the attachment bolt in those situations where the cable, pipe, angle iron or strut type seismic braces are pulling at an angle relative the axis of the attachment bolts or rods.